The present invention relates to novel parathyroid hormone peptide derivatives useful in hormone therapy.
Parathyroid hormone (PTH) is synthesized in the parathyroid, and plays an important role in controlling blood calcium concentrations or phosphoric acid ion concentrations by acting on the bone, the kidney and the intestine which are its target organs. PTH is a peptide hormone consisting of 84 amino acids, and the biological action thereof can be reproduced by a peptide fragment of an N-terminal (1 through 34 amino acid) portion, G. W. Tregear et al., Endocrinology 93, 1349-1353 (1973).
The amino acid sequence of the peptide fragment of the N-terminal (1 through 34 amino acid) portion of this human type PTH (this peptide fragment is hereinafter abbreviated as human PTH(1-34) or hPTH(1-34)) is as follows: ##STR2##
From the biological action of PTH, it is expected that the use of PTH as a drug will provide a drug useful for various bone diseases and the like. However, the following properties of the peptide make it difficult:
(1) The peptide is easily decomposed by various enzymes within the body; PA1 (2) The absorption efficiency of the peptide into the body through various routes is very low; and PA1 (3) The peptide is unstable to various physicochemical conditions such as oxidation. PA1 (1) a peptide represented by general formula [I] or a salt thereof: ##STR3## wherein R.sub.1 represents Ser or Aib; R.sub.2 represents Met or naturally occuring hydrophobic amino acid; R.sub.3 represents Leu, Ser, Lys or an aromatic amino acid; R.sub.4 represents Gly or a D-.alpha.-amino acid; R.sub.5 represents Lys or Leu; R.sub.6 represents Met or naturally occurring hydrophobic amino acid; R.sub.7 represents Glu or a basic amino acid; R.sub.8 represents Val or a basic amino acid; R.sub.9 represents Trp or 2-(1,3-dithiolane-2-yl)Trp; R.sub.10 represents Arg or His; R.sub.11 represents Lys or His; R.sub.12 represents Lys, Gln or Leu; and R.sub.13 represents Phe or Phe-NH.sub.2. However, except that simultaniously R.sub.1 consists of Ser, R.sub.2 consists of Met, R.sub.3 consists of Leu, R.sub.4 consists of Gly, D-Ala or D-Pro, R.sub.5 consists of Lys, R.sub.6 consists of Met, R.sub.7 consists of Glu, R.sub.8 consists of Val, R.sub.9 consists of Trp, R.sub.10 consists of Arg, R.sub.11 consists of Lys and R.sub.12 consists of Lys (SEQ ID NO:2).
In order to solve such problems and to understand the relationship between structure and activity of the above hormone, various derivatives have been synthesized for the PTH(1-34) fragment. While, such syntheses have been conducted for bovine PTH(1-34), few examples are known for the human PTH(1-34). For example in one such derivative, when the C-terminus Phe of the human PTH(1-34) is converted to Phe-NH.sub.2, an increase in activity is observed (Japanese Patent Unexamined Publication No. 58-96052). This increase in activity is believed to be due to inhibition of carboxypeptidase which decomposes the hormone. Further, human PTH(1-34) contains two Met residues. A molecule in which these Met residues are substituted with Nle residues prevents the hormone from losing its activity due to oxidation (Japanese Patent Unexamined Publication No. 61-24598).